Gaseous fuel powered engines are common in many applications. For example, the engine of a locomotive can be powered by natural gas (or another gaseous fuel) alone, or by a mixture of natural gas and diesel fuel. Natural gas may be more abundant and, therefore, less expensive than diesel fuel. In addition, natural gas may burn cleaner in some applications.
Natural gas, when used in a mobile application, may be stored in a liquid state onboard the associated machine. This may require the natural gas to be stored at cold temperatures, typically about −100 to −162° C. The liquefied natural gas (LNG) may then be drawn from the tank by gravity and/or by a boost pump and directed to a high-pressure pump. The high-pressure pump further increases a pressure of the fuel and directs the fuel to the machine's engine. In some applications, the liquid fuel is gasified prior to injection into the engine and/or mixed with diesel fuel (or another fuel) before combustion.
One problem associated with high-pressure pumps involves reducing leakage of fuel past pistons of the pump. Although generally tight tolerances between the pistons and associated barrels can be maintained to reduce leakage, such tolerances can also increase friction between the pistons and barrels. This friction requires more energy to drive the pump. Pumps can also have seals between the pistons and barrels to help reduce leakage. The seals can wear over time, thereby reducing the lifespan of the pump.
One attempt to improve sealing around. a piston of a pump is disclosed in U.S. Pat. No. 4,813,342 (the '342 patent) that issued to Schneider et al. on Mar. 21, 1959. in particular, the '342 patent discloses a piston for a reciprocating pump that pressurizes cryogenic fluids. The piston has a core attached to a push rod of the pump. The core includes a shaft that has flanged ends and is surrounded by a sleeve between the flanged ends. Between the sleeve and each of the flanged ends of the shaft are seal rings and expanding members that have higher coefficients of thermal expansion than the sleeve. When the piston is cooled and the core shrinks axially, the flanged ends of the shaft are drawn into the expanding members, which push outwardly on the seal rings to create a seal between the piston and a barrel cylinder of the pump.
While the piston of the '342 patent may have reduced leakage, it may still exhibit a significant amount of friction. Further, the expanding members of the core may increasingly push the associated rings against the cylinder, which increases wear of the rings.
The disclosed piston is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.